1. Field of the Invention
The invention relates to a method for controlling a level of a voice signal, which is demodulated by a frequency modulation receiver, and a level-controlling device.
2. Description of the Related Art
The received RF(Radio Frequency) signal strength from a base station in a frequency modulation (FM) mode cellular phone fades intensively and dramatically in response to a change in the distance between the base station and the cellular phone or diffraction or reflection of radio wave by buildings. Noise added on a demodulated voice signal, is also fades intensively and dramatically in response to changes in the the received RF signal strength. As a result, the voice signal from the communicating party has a poor sound quality. Conventionally, a level-controlling circuit for a the voice signal in FM mode cellular phone controls the level of the voice signal in response to the received RF signal strength which is detected by a received RF signal strength detecting circuit. Concretely, The method utilized is that the level of the level of demodulate voice signal is attenuated by the received RF signal strength. For example, in a case that the received RF signal strength is weak, and high level of noise is superimposed on the voice signal, the voice signal and the noise are decayed.
However, in the conventional level-controlling circuit mentioned above, the level of the demodulated voice signal changes frequently in response to changes in the received RF signal strength. Therefore, the voice of the communicating party breaks up for short periods, or for long periods.